Abrasive article



Nov. 17, 1931. D, WEBSTER 1,832,515Av ABRAsIvE ARTICLE Filed March 16, 1951 Fla] Patented Nov. 11, 1931 UNITED STATES rATENT oFElcE pUANE n wTiEsTEn, or WORCESTER. MASSACHUSETTS, as sIGNoa To NORTON comm, or WoncEsTEn, nAssAcnUsnTTs, A oonronATIoN or mAssAcnUsETTs ABBASIVE .ARTICLE Application led Iareh 16, 1931. Serial No. 528,0013.

My inyention relatesto grinding wheels and more particularly to' a ring wheel for use in a disk grinding machine in which it is supported to provide' an annular, plane grinding surface.

One type of grinding wheel for this purpose comprises a metal backing disk to the end face of which a-suitable grinding mem.- ber, of granular abrasive material bonded by an organic or vitried ceramic bond, is secured by a cementitious material, such as shellac or resin cement and the like. Suitable devices, such as projecting studs, are provided in the backing disk for attaching the wheel to a metal supporting disk carried by a rotatable driving shaft. Her'etofore, in the manufacture of wheels of this type, it is not uncommon to 'ind that. the grinding member has become loose from its metal backing or that serious structural cracks and ruptures have formed in the abrasive body/, itself. It is found thatthese defects ordi narily occur when the assembled Wheel is 5 removed, while hot, from the baking oven in which the resinous cement has been sub. jected to a heat hardening operation. On cooling to room temperature, stresses are produced in the warm mass, due to .shrinkage or the like. which arise from the great difference in the coefficients 'of expansion of the abrasive bond and the metal constituting the support for the grinding member. Even if not badlv cracked when initially manufactured. these fragile grinding members mav be defective and later break during the grinding operation while the wheel is in use. Such breakage may mean a considerable loss to the user1 hence every effort has been made to prevent the occurrence `of such eXtremethermal stresses, but due to difficulties inherent in the processes of manufacture and the natural physical properties of the materials which must be considered. it has not r. been lound possible t`o do so at all times. It is accordingly an object of .my invention to overcome such diculties and to provide a rinding wheel construction which is capab e of being easily manufactured and Y will not develop such detrimental defects..

A further object of my invention is to employ a wheel construction in which the parts will be integrally united to form a unitary body whereby the thermal changes due to expansion and contraction will be evenly and uniformly distributed throughout.

In accordance with my invention I propose to make an abrasive article, such as a grinding wheel, inthe form of a composite or laminated structure in which an abrasivebodv composed of granular abrasive material combined with an organic bond, such as a ysynthetic resin or resinoid, is integrally united with a self-supporting backing of a hard, unyielding, organic composition which comprises substantially the same material as the wheel bond and the backing and has substantially the same coefiicient of expansion. In my preferred form the backing comprises a resinoid body, which may be reenforcedby al strengthening member embedded therein. and an abrasive bodv of resinoid bonded abrasive grains united t0 forma unitary body. The backing and abrasive mav be formed integrally in a single operation Without an intermediate bodv of cement or the twoparts may be initially molded separately and then united by a cement. In either case. the bond, backing and cement will have snbstantiallv the same coeiiicients of expansion and will preferably comprise the same resinoid. As one manner of carrying out this invention, I make use ofa synthetic resin of the phenolic condensation type as is obtained by the reaction of phenol or it's homologues with formaldehyde and which is capable of being converted to form an unusually tenacious bond when suliiciently heated to produce the final reaction.` l i In the drawings Awhich illustrate one ernbodiment of this invention and in which like reference numerals indicate like parts:

Fig. 1 is a plan view of a grinding wheel embodying my invention; and

Fig. 2 is asectional view, taken on the line 2 2 of Fig. 1, of the assembled wheel when ready for use.

As-illustrated, the abrasive body may be Amade up in accordance with standard practice, such as disclosed in the patent to Brock No. 1,537,454 of May 12, 1925, of a preformed abrasive annulus or ring 10 having a plane grinding surface 11 and composed of granular abrasive material, such as crystalline alumina or silicon carbide, bonded by a synthetic resin composed of a heat hardening condensation product, such as one of the type commonly known under the trade-mark Bakelite. Hereafter, these resin condensation products will be referred to as resino ids, so designated in the art on account of their characteristic difference from the properties common to the natural resins in that they polymerize and harden upon heating to a form that is hard, infusible and insoluble.

In order to support the abrasive annulus rigidly so that it may be mounted directly on the end of a rotating shaft, I provide a backing support for the wheel which isintegrally united to the grinding ring so as to form a unitary grinding body. The type of backing l i support shown in the drawings comprises a disk 15 having a reticulated reenforcement .35 therein, which possesses sufficient strength and rigidity to support the abrasive annulus during the grinding operation and is adapted to be mounted on a rotating shaft (not shown) by means of an outer hub 16. In my preferred construction thedisk 15 may be made of a material commonly known under the trade-mark Micarta?, which comprises a preformed molded body. made up of layers of fabric or other reenforcing material of suitable'thickness which is cut to the desired shape, and then impregnated with a resinoid binding media, more particularly a phenolic resin, such as Bakelite resin. The impregnated material is then subjected to heavy pressure by which the various sections are intimately joined together aswell as shaped, after which it is subsequently baked to harden the resin. The backing member, when completed, will. constitute the sole support for the wheel structure and will be directly mounted upon the rotatable driving s indle.

To this end, the hub 16 is provided with an exterior surface of the proper size and i of the required shape to fit within and be clamped against the inner vperipheral surface of a suitably shaped collar (not shown) adapted to support the wheel on the rotating shaft. The disk 15 is provided with a central aperture 18 adapted to fit over the end portion of the rotatable shaft. In close proxunity to this aperture there are provided a series of holes 20 adapted to receive suitable clamping screws or bolts which may pass through the backing disk and into the collar tpl titereby fasten the grinding wheel to the s a In order that the grinding ring may fit properly against the backing disk, the outer surface of the abrasive face opposed to the disk is provided with a hub portion 22 which is of the proper size to fit within a correspondingly shaped depression or cavity 23 formed in the opposed face of the backing disk 15. When assembled, the interttting faces of the annulus and the backing disk respectively provide the opposed surfaces with a large area of contact and thus enablel the parts to be more firmly united by the securing medium.

lVhile the grinding ring may be formed in situ on the backing after the latter has been fully made, or the two parts may be molded of the green material and all of the resinoid be heat set in a single operation, yet in my pre.

ferred form the abrasive annulus and the backing are first initially.made in vseparate operations and then cemented together. To this end, I propose to placea layer of a suitable cement itious organic material 25 between the juxtaposed faces vof the abrasive ring` backing member. Tor this end, thecement may comprise a mixture of a resinoid, such as Bakelite, and a suitable plasticizing agent, such as furfural, acetone, etc., the latter being employed in amounts sufficient to produce a mass of the desired plasticity.

Upon the application of heat, the composition will reactl to form an inusible, insoluble condensation product with the annulus and its backing disk integrally joined together toform a unitary inflexible grinding body. In practice, the cement layer may be applied to the bonding face of either the preformed annulus or the backing disk, prior to their assembly. The parts are thereafter assembled and the structure subsequently heat treated at a temperature sufficient to mature the resinous material.

In order that the grinding ring may be more securely and intimately held to the backing disk by the resinous layer, the disk may be provided with a series of holes 30 which extend through the disk and are countersunk on the back face so as to appear as an inverted 'frustum of a cone, the small end of which is adjacent to the juxtaposed face of the grinding annulus.` n assembly of the parts` the layer of resin cement will flow into and fill the countersunk holes, thus forming a' series'of tapered or frusto-conical dowels of the resinous material which integrally unites and bonds with the disk during the final baking operation.

It will of course be understood that the parts may be united lin any other desired manner. yF or example, it is feasible, after placing a preformed backing disk in a mold,

`to coat the bonding face of the disk with the resin cement and then mold an abrasive annulus thereto from a suitable mixture of abrasive grains and the Bakelite resin powder ander heat and pressure. The article may then be removed from the mold and thereafter baked to mature the resin. Like- Wise, the cement layer may be omitted, and the .resinoid bond used with the abrasive grains will unite the parts integrally. In that case the mixture of abrasive grains with resinoid bond, and a plasticizing medium. such as furfural, may be placed on the preformed Micarta backing and the parts then pressed and heat hardened. The abrasive body and associated parts may be made in accordance with standard practice, such as that described in the patent to Martin No. 1,626,246 of April 26, 1927. This type of grinding wheel possesses marked advantage over one made of other materials which have heretofore been employedfor such purposes. The various portions of the wheel structure are ma-de of the same type of bond which, when matured, results in a unitary structure integrally united by a single tenacious bond. The difference of coefficient of expansion between the various parts is diminished substantially to zero value by the proper selection of the bonding ingredients used, and the structure will accordinglv be free from the strains which such differences set up when the article is subsequently heated or cooled, By so constructing such a Wheel to prevent serious losses due to breakage and rupture. I have made it feasible to manufacture the ring wheel more successfully and to a greater extent than heretoforeobtainable.

While I have specifically described my invention as adapted to the manufacture of an abrasive wheel of a phenolic resin composition it will be obvious to those skilled in the art that other abrasive articles in which the same or similar properties are desired may be made and that other materials may also be used throughout the structure to suit the particular conditions which may in the case be involved. Such modifications or substitutions of my invention as lie within the scope of the. appended claims are, however, to be considered as embodied in the above specification.

Having thus described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A grinding wheel comprising an abrasive body of abrasive grains containing a resinoid bond uniting the grains into a unitary mass and a rigid reenforcing backing therefor comprising a resinoid integral with the bond of the abrasive body, said backing being the sole support for the abrasive body and directly mounted upon a rotatable driving spindle. y

2. A grinding wheel comprising an abrasive body of abrasive grains containing a resinoid bond uniting the grains into a unitary mass and a backing therefor, which comprises a rigid resinoid body and which is integral With and has substantially the same coetiicient of expansion as the bond of the abrasive body.

3. A grinding wheel comprising an abrasive body of abrasive grains containing a resinoid bond uniting the grains into a unitary mass and a backing therefor, which comprises a rigid resinoid body containing layers of reenforcing material, and which is integral With the bond of the abrasive body, said body and the backing each having substantially the same coefficient of expansion.

4. An'abrasive article comprising a resinoid body, an abrasive member of resin bonded abrasive grains, and a layer of cementitious organic material between and integrally uniting the bonded abrasive member with, said resinoid body.

5. An abrasive wheel comprising a rigid resinoid body containing reinforcing layers of reticulated material. and an abrasive member of bonded abrasive grains integrally united thereto and having an abrading surface.

6.1 An abrasive wheel comprising a rigid non-abrasive resinoid body and an abrasive member of resin bonded abrasive grains having an end face opposed to said body and integrally united therewith, the opposite end face of said abrasive member providing a plane grinding surface for the wheel.

7. A laminated abrasive article having an abrading facing of phenolic resin bonded abrasive grains, a hard resinoid backing layer, and an intermediate layer of cementitious material matured therebetween and integrally uniting said facing and the backing.

8. An abrasive wheel comprising an abrading body of phenolic resin bonded abrasive grains, a rigid resinoid backing support therefor containing reenforcing layers of fabric, and a cementitious medium between and integrally uniting said backing support and the abrading body embodying a resinoid sustantially identical with that contained in the abrading body and the backing support.

9. A composite grinding wheel comprising an abrading body of resinoid bonded abrasive grains, a rigid backing of resinoid material, and a layer of cementitious resinoid material therebetween and integrally uniting said body and backing to fornr a unitary rigid grinding structure 1n which the resinoid for the various portions has substantially the same coeicient of expansion.

l0. A. grind-ing wheel comprising a grinding annulus of resinoid bonded abrasive 5 grains, a rigid support therefor of disk-like shape containing a resinoid and integrally united to said annulus, and means-central with said support which constitutes the sole rotatable support of the wheel structure during grinding.

Signed at Worcester, Massachusetts this 13th day of March 1931. d

DUANE E. WEBSTER4 

